The present invention relates to a novel polymerizable liquid crystalline oxetane compound, a polymerizable liquid crystalline composition containing such a liquid crystalline oxetane compound, a method for producing a liquid crystal film using such a polymerizable liquid crystalline composition, an optical film comprising such a liquid crystal film produced by such a method, and a liquid crystal display equipped with such an optical film.
Active studies and developments have been carried out to utilize liquid crystalline compounds as optical materials, and many of them have been already put into practical use. In order to apply a liquid crystalline compound to an optical material, it is essential that after the compound is fixed in an aligned liquid crystal structure, it can be retained in the fixed aligned structure under practical use conditions. As methods for retaining the fixed aligned structure of a liquid crystalline compound, there have been proposed various methods wherein to use polymerizable liquid crystalline compounds, to use polymeric liquid crystalline compounds, and to use polymeric liquid crystalline compounds having crosslinkable reactive groups.
Japanese Patent Laid-Open Publication No. 11-080081 discloses a method using polymeric liquid crystalline compounds having crosslinkable reactive groups, such as those having a mesogen portion comprising two or more benzene rings or similar rings, spacer portions each comprising a hydrocarbon chain, and radically polymerizable reactive groups such as (meth)acrylate group at one or both of the terminal ends. In this method, a polymerizable liquid crystalline compound is coated in a heat-melted state or in the form of a solution on an alignment substrate to be formed into a liquid crystal layer and dried if necessary. Thereafter, the liquid crystal layer thus formed is aligned in a liquid crystal orientation by heating and then polymerized by photo-irradiation so as to fix the liquid crystal orientation. However, this method is required to suppress an undesired polymerization inhibition effect caused by oxygen in the air and also needs some complicated operations such as a photo-irradiation under an inert gas atmosphere and improved facilities and apparatus in connection with such complicated operations. Since (meth)acrylate group is easily polymerizable with light or heat, a careful attention must be paid during the synthesis.
As disclosed in Japanese Patent Laid-Open Publication No. 11-158258, there is a method using polymeric liquid crystalline compounds, such as liquid crystalline polyesters excellent in capability of retaining an aligned liquid crystal orientation. However, due to the wide-spread of mobile communication tools, optical films formed from liquid crystalline polyesters are demanded to have a retainability of the aligned structure under more sever conditions and to be more in excellent mechanical strength.
As methods using polymeric liquid crystalline compounds having polymerizable reactive groups, Japanese Patent Laid-Open Publication No. 9-3454 proposes a method wherein polymerizable reactive groups are introduced into the main chain of a polymer and a method wherein a monomer unit having polymerizable reactive groups are introduced into the side chain(s). However, since the liquid crystallinity of the compounds is reduced in either of the methods, there is a limit to introduce polymerizable reactive groups in such a large amount that the mechanical strength is sufficiently enhanced. Therefore, alternative methods have been demanded.